1. Field of Invention.
The present invention relates to an article of manufacture using radiofrequency energy to catalyze the removal of gaseous pollution contaminants, such as soot, NO.sub.x, CO and hydrocarbons.
2. Background.
A gaseous stream, often obtained from some combustion or heating process, contains many substances that are potentially classified as pollution contaminants, such as soot, NO.sub.x, CO and hydrocarbons.
Soot is a substance usually associated with carbonaceous material formed upon incomplete combustion. It is black, messy and sometimes "feels" oily because of the large amount of hydrocarbons clinging to the base carbon material. A common source of soot is the exhaust from a diesel engine and such soot is visible from many diesel trucks particularly under acceleration. Another common use of diesel engines is for mining where such engines are employed to power underground transportation equipment. In all instances soot is considered an unwanted substance that presents environmental problems since carcinogenic compounds are often found in diesel exhaust adsorbed upon such soot. Additionally some trace quantities of metallic compounds are often found in soot. Most aerosol associated with soot is most likely under one micrometer in size; therefore, it generally is respirable and can cause lung damage.
The U.S. Bureau of Mines estimated that more than ninety percent of the measured aerosol under one micrometer in size in mine atmospheres came from diesel exhaust. Further the average concentration of diesel particulate matter varied from 0.53 to 1.2 mg/m.sup.3 in such mines.
Another product of combustion is various nitrogen oxides, usually given the symbol NO.sub.x since their molecular form often is unknown. NO.sub.x is a common constitute of smog in many cities and its control often is mandated by federal law. A further product of combustion is carbon monoxide, CO, which is poisonous and so unwelcome in exhaust gases.
In many instances gases that are exhausted contain various hydrocarbons either from incomplete combustion of fuels or from the non-combustion heating of organic material. An example of the latter case is the exhaust coming from a cooking grill where the heating of meat and other organic material drives of various hydrocarbons, and often such hydrocarbons condense in cooler parts of the exhaust system and represent a fire hazard. In other instances hydrocarbons from incomplete combustion contribute to the smog problem.
The subject invention is a pollution arrestor. In this writing `pollution arrestor` is defined as `an article of manufacture through which a polluted gas is passed in order to reduce the concentration of unwanted contaminants.` In the subject invention such reduction or removal is by chemical means whereby said contaminants undergo chemical reactions to convert them into non-polluting forms. Such reactions use catalytic means including radiofrequency (RF) energy catalysis employing specific forms of carbonaceous material that are energized by RF energy. Such equipment is often in the form of a cartridge that is inserted into an appropriate RF field.
Quantum radiofrequency physics is based upon the phenomenon of resonant interaction with matter of electromagnetic radiation in the microwave and RF regions since every atom or molecule can absorb, and thus radiate, electromagnetic waves of various wavelengths. The rotational and vibrational frequencies of the electrons represent the most important frequency range. The electromagnetic frequency spectrum is conveniently divided into ultrasonic, microwave, and optical regions. The microwave region runs from 300 Mhz (megahertz) to 300 Ghz (gigahertz) and encompasses frequencies used for much communication equipment. For additional information refer to N. Cook, Microwave Principles and Systems, Prentice-Hall, 1986.
Often the term microwaves or microwave energy is applied to a broad range of radiofrequency energies particularly with respect to the common frequencies, 915 MHz and 2450 MHz. The former is often employed in industrial heating applications while the latter is the frequency of the common household microwave oven and therefore represents a good frequency to excite water molecules. In this writing the term `microwaves` is generally employed to represent `radiofrequency energies selected from the range of about 915 to 5000 MHz,` since in a practical sense this total range is employable for the subject invention.
The absorption of microwaves by the energy bands, particularly the vibrational energy levels, of the atoms or molecules results in the thermal activation of the nonplasma material and the excitation of valence electrons. The nonplasma nature of these interactions is important for a separate and distinct form of heating employs plasma formed by arc conditions of a high temperature, often more than 3000.degree. F., and at much reduced pressures or vacuum conditions. For instance, refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Supplementary Volume, pages 599-608, Plasma Technology. In microwave technology, as applied in the subject invention, neither condition is present and therefore no plasmas are formed.
These microwaves lower the effective activation energy required for desirable chemical reactions since they can act locally on a microscopic scale by exciting electrons of a specific atom in contrast to normal global heating by raising the bulk temperature. Further this microscopic interaction is favored by polar molecules whose electrons become locally excited leading to high chemical activity; however, nonpolar molecules adjacent to such polar molecules are affected to a much lesser extent. An example is the heating of polar water molecules in a common household microwave oven where the container is of nonpolar material that is microwave-passing and stays relatively cool.
A polar material interacts with microwaves readily and rapidly degrades its effective penetrating power. This aspect is employed in waveguides for microwave transmission since the waveguide transmits the energy along the skin of the guide; therefore, the guide is hollow. Such a hollow waveguide contains a substantially uniform energy field that is utilized particularly for laboratory experiments. However in the subject invention a more commercial version is required that is low cost to make and operate.
As used above microwaves are often referred to as a form of catalysis when applied to chemical reaction rates. For instance, see Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume 15, pages 494-517, Microwave Technology.
Related United States patents using microwaves include:
______________________________________ U.S. Pat. No. Inventor Year ______________________________________ 4,076,606 Suzuki et al. 1978 4,345,983 Wan 1982 4,545,879 Wan et al 1985 ______________________________________
Referring to the above, Suzuki et al. disclose a process for homogeneously, not hetrogenously, decomposing NO.sub.x using microwave irradiation at the standard microwave frequency in an exhaust gas without any adsorbent present with a preprocessing step of removing sulfur compounds. With no impure carbon material present, no microwave catalysis is occurring and the microwave energy merely excites the nitrogen molecule in a homogeneous gaseous medium.
Wan discloses a method for decomposing solid chlorinated hydrocarbons with a ferromagnetic catalyst using ordinary microwave heating, not microwave catalysis.
Wan et al disclose employing ordinary microwave heating, not microwave catalysis, to desulphurize pulverized petroleum pitch using a ferromagnetic catalyst.